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Went to street legals last Sunday and my 69SS launched great, pulled hard until about 1000 feet, then fell on it's face. Every pass. Best time was [email protected] 1.62 60ft. Usually runs easy mid 11's or quicker. Ran great last year on same fuel setup, only thing I changed was jetted down the primaries from 76s to 72s but that shouldn't cause it to lean out like that or would it? Holley 140gph electric pump, Aeromotive regulator with return line, 6an lines. 950 Quick Fuel with jet extensions. I noticed my fuel pressure was only 2psi after my first pass so cranked it up every pass which improved the times but still something wrong here. Last year was set at 6.5psi. No idea how it would change but I am no tuning genius. Eventually left it at 7psi. Fuel filter is new so I have no idea wth is wrong. One more track day this coming Sunday so want it to work. Any ideas gentlemen?
 

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whats the fuel pressure when power cuts off?

Pump might give in..

Your setup should be sufficient, proven by yourself last year. So it might be a malfunction of some unit along the fuel line..
 

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Went to street legals last Sunday and my 69SS launched great, pulled hard until about 1000 feet, then fell on it's face. Every pass. Best time was [email protected] 1.62 60ft. Usually runs easy mid 11's or quicker. Ran great last year on same fuel setup, only thing I changed was jetted down the primaries from 76s to 72s but that shouldn't cause it to lean out like that or would it? Holley 140gph electric pump, Aeromotive regulator with return line, 6an lines. 950 Quick Fuel with jet extensions. I noticed my fuel pressure was only 2psi after my first pass so cranked it up every pass which improved the times but still something wrong here. Last year was set at 6.5psi. No idea how it would change but I am no tuning genius. Eventually left it at 7psi. Fuel filter is new so I have no idea wth is wrong. One more track day this coming Sunday so want it to work. Any ideas gentlemen?
When your fuel pressure drops like that for no reason change your fuel filter. I had that happen in 2014. The year prior 6.5 Psi and the next race a year later 6.5 through 1st gear and dropped to 3 psi. Changed the filter and stayed at 6.5 until I revamped my fuel system.
 

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Discussion Starter · #6 ·
When your fuel pressure drops like that for no reason change your fuel filter. I had that happen in 2014. The year prior 6.5 Psi and the next race a year later 6.5 through 1st gear and dropped to 3 psi. Changed the filter and stayed at 6.5 until I revamped my fuel system.
I will give it a try. At worst I will have a spare filter. Thanks
 

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I will give it a try. At worst I will have a spare filter. Thanks
For me with the car just racing and no street time I thought there was no way the filter could be plugged. Boy was I wrong on that one. What brand of filter do you run?
 

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Remove the sock filter in the tank, use a high flow inline one before the tank instead.

Also, if you leaned the primary jets that much, in order to maintain your wot AFR, you would need to open up the PVCR jets the same amount you reduced the jets by. A 76 to 72 jet is .005" smaller. So you would need to drill out the PVCR by .005".

Also, if you have a liquid pressure gauge under the hood, the reading will drop as it heats up. Set pressure when you first start the car and it's cold.
 

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Picked up a new filter and AFR gauge today so I can actually tune this thing instead of guessing. Putting the 76s back in the primaries and give it a try this Sunday hopefully.
76 seem kind of lean for that QF 950, most sites show them having a 84-86 jet. Do you have a P/V in the rear metering block? that would be a good reason it would have a 76 jet.
 

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Discussion Starter · #14 ·
76 seem kind of lean for that QF 950, most sites show them having a 84-86 jet. Do you have a P/V in the rear metering block? that would be a good reason it would have a 76 jet.
I really can't remember if there is a power valve in the rear metering block. Can't remember if it came with 76s in the primaries or if I installed them. I think I swapped them in. I have to start writing some of this stuff down LOL. Once I get the AFR gauge set up I will start being more precise with my tuning.
 

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Discussion Starter · #16 ·
Might be a good idea to do a volume test, unhook fuel line at the carb and run it into a a jug and see how much get. Wouldn’t hurt to check the tank vent.
Try new filter and jet it up first. Nothing else has been changed and fuel system in pretty much new. Worked great last year. If not will keep trying things you guys have suggested. Not much time left this year. Winter is coming quick I think.
 

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Try new filter and jet it up first. Nothing else has been changed and fuel system in pretty much new. Worked great last year. If not will keep trying things you guys have suggested. Not much time left this year. Winter is coming quick I think.
Know what you mean, all I have to show for my efforts so far this year is a lousy [email protected], a definite down turn from last year after an intake and converter swap so far. I only have 3 times to test this year, damn rain.
 

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Went to street legals last Sunday and my 69SS launched great, pulled hard until about 1000 feet, then fell on it's face. Every pass. Best time was [email protected] 1.62 60ft. Usually runs easy mid 11's or quicker. Ran great last year on same fuel setup, only thing I changed was jetted down the primaries from 76s to 72s but that shouldn't cause it to lean out like that or would it? Holley 140gph electric pump, Aeromotive regulator with return line, 6an lines. 950 Quick Fuel with jet extensions. I noticed my fuel pressure was only 2psi after my first pass so cranked it up every pass which improved the times but still something wrong here. Last year was set at 6.5psi. No idea how it would change but I am no tuning genius. Eventually left it at 7psi. Fuel filter is new so I have no idea wth is wrong. One more track day this coming Sunday so want it to work. Any ideas gentlemen?
What prompted you to jet down from 76 to 72 ? If it ran better Before that change and that is indeed the only thing that you did change then id go back the other way .
Put it back to 76 and see what it does ..
76 is your baseline . Make changes one at a time and then see what difference(if any ) it makes. Sometimes swinging way lopsided in one direction and the other can tell a story.
 

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Running an air cleaner? I did run without one once and the primary air vent on the carb ingested a wasp. Flooded and caused other grief until we found it.
 
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